Electromagnetic heating unit



1967 c. F. SCHROEDER ELECTROMAGN TIC HEATING UNIT Original Filed Nov. 30, 1962 5 Sheets-Sheet l Feb. 28, 1967 c, SCHRQEDER 3,307,008

ELECTROMAGNETIC HEATING UNIT Original Filed Nov. 30, 1962 3 Sheets-Sheet 2 iiillllllllllllllllll INVENTOR. (mm 5 E Swim-am Feb. 28, 1967 C- F. SCHROEDER ELECTROMAGNETIC HEATING UNIT 3 Sheets-Sheet 5 Original Filed Nov. 30, 1962 INVENTOR. Scwomm mm 55 f United States Patent Qfifice 3,307,008 ELECTROMAGNETIC HEATING UNIT Charles F. Schroeder, 2317 Valleybroolr Drive, Toledo, Ohio 43615 Original application Nov. 30, 1962, Ser. No.

[Patent No. 3,265,851. Divided and Oct. 23, 1965, Ser. No. 503,504

6 Claims. (Cl. 21.9-10.49)

241,208, now this application This application is a division of my c opending application Serial No. 241,208, filed on November 30, 1962, now Patent No. 3,265,851.

The present invention relates to an electromagnetic transformer unit, and more particularly, a heater unit utilizing a closed secondary winding in such manner as to make the unit adaptable to performance in a wide range of specific devices for different heating purposes.

According to the present invention, a magnetic circuit construction is provided which, although capable of design for operation at any of a wide range of frequencies, is highly adaptable to the translation of electrical energy into heat energy at the usual commercial frequencies of 50 or 60 cycles and even lower frequencies, such as 25 cycles still occasionally encountered in practice.

It is a purpose of the invention to provide a magnetic circuit construction incorporating principles which make it adaptable to provision of heating units for translation of electrical energy into heat energy at commercially available power, frequencies equipment.

It isanother object of the invention to provide a new electrical heating unit flexibly adaptable to any of a wide varietyof uses by proportional changes in shape within the. latitude of variation permitted by the principles employed.

In brief, the operating elements of the construction of the invention include a magnetic core energized by a primary winding, and a single turn secondary loop which surrounds both the core and primary to provide a heating unit arrangement flexibly utilizable for either home appliance or industrial purposes. This is accomplished in general by surrounding a magnetic circuit loop with a secondary, not only closed about the cross section of the core, but also extending along the length of the magnetic circuit and forming a closed loop.

A feature of the invention lies in its adaptability in design to practically anycommercial voltage and frequency without need for special auxiliary frequencygenerating equipment.

Another feature of the invention lies in its ruggedness of construction and adaptability to provision of selective surface areas to be heated to high temperatures, while other portions of the unit remain substantially cool.

Still another feature of the construction of this invention lies in its efiiciency in translation of electrical energy into heat energy, and the adaptability of the principles to practically any size construction.

Although for purposes of illustration, this invention is herein described in connection with the translation of electrical energy into heat, it'will be understood upon review of the embodiments disclosed, that they are adaptable for other purposes as well, such for example, as where large magnet flux concentrations are desirable and are produced :as a result of high currents in the closed secondary loop.

Other objects and features which are believed to be characteristic of my invention are set forth with particularity in the appended claims. My invention, however, both in organization and manner of construction, together with further objects and features thereof, may be best understood by reference to the following description with a minimum of cost in,

3,307,003 Patented Feb. 28, 1967 taken in connection with the accompanying drawings, in which: 7

FIGURE 1 is an isometric view, partially broken away and partially in cross-section, illustrating a magnetic circuit construction embodying the principles of my invention;

FIGURE 2 is an isometric view, partially broken away and partially in cross-section, of an electrically heated kettle embodying the magnetic circuit principles of my invention; 7

FIGURE 3 is a partially broken away and partially crosssectional view of an extrusion press cylinder embodying a plurality of magnetic circuit sections according to the principles of my invention;

FIGURE 4 is an isometric partially broken crosssectional view of a hot-plate type unit embodying the principles of the magnetic circuit construction of this invention;

FIGURE 5 is an isometric broken cross-sectional view of a fry-pan construction embodying the closed secondary magnetic circuit principles of the present invention;

FIGURE 6 is a somewhat schematic isometric view partially broken away and partially in cross-section of a heater strip embodying the principles of the present invention;

FIGURE 7 is an enlarged broken cross-sectional view a portion of the heater strip of FIGURE 6; and FIGURE 8 is a semi-schematic illustration of a heating unit embodying the principles of the present invention adapted to integral association of a temperature control circuit.

Referring to the drawings in greater detail, FIGURE 1 shows the general arrangement of components of a transformer type construction 10 employing a single turn secondary loop wherein the single turn loop comprises the outer shell made up of an annular member of U-shaped cross-section capped by a flat ring-shaped capping ember which forms an enclosure and completes a closed electrical loop for an annular magnetic core 13 residing therein. The ring-shaped cap 12 and the annular U-shaped member 11 are both of electrically conducting material such as aluminum, steel, copper, zinc, etc., capable of permitting a low resistance juncture of the ring cap 12 and the member 11 to establish a low resistance loop about the magnetic core enclosed therein. The magnetic core 13 is made up of magnetic flux path segments and in this respect, can for example, be a spiral-wound core or a series of stacked annular discs or even a magnetic wire wound core. The primary or energizing winding 14 is wound directly on the core over electrical insulation of high temperature-resistant properties. The primary winding as illustrated may extend over the full length of the core, and correspondingly extend through the interior of the annular secondary for its entire length. The leads 15 for the primary winding 14 are connected to plugtype connector prongs 17 mounted on an insulating member 16 installed in the side of the annular secondary.

FIGURE 1 illustrates that the annular members 11 and 12, in a sense, form a pair of secondary loops. One closed loop is formed by the cross-sectional path of the shell for the core 13, while the other loop is provided longitudinally by the annular shape of the shell.

In operation, energization of the primary winding 14 generates a magnetic flux in the core 13. This flux cuts the walls of the surrounding shell and generates a sec ondary current having a path extending around the crosssection of the shell. This is illustrated by the dashedline loop drawn in the shell wall in FIGURE 1. Since the magnetic flux alternates, the current flow in the crosssectional loop is also alternating. Accordingly, double headed arrows are utilized to illustrate the path of flow of such current. Any tendency toward flux leakage diametrically across the annular core results in generation of an annular current flow, in addition to the flow in the cross-sectional loop. Sufficient current can be readily made to flow, particularly in the cross-sectional loop, to result in the temperature of the unit being raised to a degree permitting its utilization as a heater unit.

FIGURE 2 shows a heating kettle embodying the principles of the transformer unit of FIGURE 1 for translation of electrical energy into heat for cooking purposes. In this embodiment, the closed loop secondary is formed of the hollow shell-like walls of the kettle made up of a thick outer wall 21 and a thin inner wall 22. Since the current flow in the secondary is predominantly in the cross-sectional loop, the current flow in the thick outer wall equals that of the thin interior wall of the kettle. Thus, when the annular-shaped core 23 encased within the cross-sectional loop is energized by the primary coil 24 wound thereon, the current flow in the cross-sectional loop will cause by far the greatest 1 R loss in the interior wall 22 effecting translation of the energy into heat. In the opposite sense, however, the outer thicker wall 21 of the cross-sectional loop can be made sufficiently thick that it will remain relatively cool while the interior wall 22 is raised to desired temperature Although the core 23 is shown extending through substantially the full height of the heating kettle, it can also be made shorter under certain electrical design criteria and not so long as to extend through the full length of the hollow walled structure. That is, the hollow interior of the unit can be made to extend a distance beyond the core and also be made narrower, if desired, to conform to desired exterior design configurations.

Upon reviewing the path of current flow in the sec ondary briefly, again it will be noted that when the magnetic flux build-up and collapse occurs within the core 23, the current flow in the closed secondary loop formed by joinder of the thin interior wall 22 to the thicker exterior through the overhanging edge of the thick wallsection 21 and its bridging bottom portion 26, can be made such that the temperature of the interior will be raised appreciably while the thicker sections 21 and 26 will not experience an appreciable rise in temperature. Thus, the exterior of the heating kettle can be maintained cool, while the interior is of sufficient temperature to heat its contents, such as food placed therein to be cooked.

To further enhance the efficiency of utilization of the kettle, the exterior can be made of relatively low electrical resistance materials such as aluminum, while the interior is made of steel having higher resistivity as well as a magnetic hysteresis which will provide a corresponding larger capability'for generation of heat with a given magnitude of current fiowinthe secondary loop. Electrical and thermal insulation 28, such as asbestos or fibrous glass, is inserted between the core 23 and the interior wall 22 to both electrically isolate the walls and to thermally insulate the core from the hot interior wall. Thus, the core, by having an interior diameter dimension somewhat larger than the diameter of the thin interior wall, is both isolated by space as well as the thermal insulation interposed therein. The interior wall and the exterior walls are joined such as by welding them together at their zone of juncture at the top of the kettle as at the bridging projection 26. If desired, the exterior can be coated with a protective layer of material such as an epoxy resin.

Handles 29 are provided at the exterior and an electrical plug 25 connected to the winding 24 is provided for convenient connection to a power source such as a 60 cycle power source.

FIGURE 3 illustrates another unit incorporating the transformer construction of my invention for heating purposes. This apparatus utilizes a series of circular transformer sections physically aligned to form a hollow cylinder such as the interior of a resin extrusion press. The

' through which material 4 common interior wall 32 of the cylinder is raised to a desired temperature while the thicker exterior which makes a series of adjacent closed loop secondaries with the interior wall 32 is maintained relatively cool. Within each closed loop secondary is a magnetic core of annular shape 33 extending about the cylindrical interior. Each core 33 is enclosed by the outer shell 31 which provides a pair of radially inwardly extending annular projections 35 located on opposite sides of the core between the shell and the interior wall 32. The interior wall '52 is sufficiently thin in dimension that it can be readily heated by current flow therethrough while the exterior shell $1 of larger thickness will not become appreciably heated by the same current. Each core 33 has an insulated primary winding 34- wound thereon while thermal insulating material is interposed between the core and the interior wall 32 of the cylinder. Thus, the core is thermally and electrically insulated from the interior wall.

The series of spaced cores along the length of the interior wall 32, are well adapted to independent energization of adjacent zones to establish different desired temperatures along the length of the cylinder. At the front of the cylinder, a nozzle 36 is provided, as shown in dotted lines, having an aperture 39 from the interior of the cylinder is extruded into a mold 37 also outlined in dotted lines. A feature of this arrangement lies in that the material extruded under pressure from such cylinder can be intimately regulated so that the material can be heated or allowed to cool to different temperatures at each stage of its path of progression along the length of the cylinder.

FIGURE 4 illustrates still another embodiment of the present invention wherein the transformer principles are utilized for generation of heat in a hot-plate typeunit. in this construction, the hot-plate unit 40 is formed of a circular electrically conducting base 41 having an annular recess therein for receipt of a magnetic core 43, also of annular shape. The core 43 has a. primary winding 44 wound thereon over its full length and energized through the exterior wall of the recess by way of leads 45 connected to suitable exterior power source. The circular base is capped by a thin plate 42 enclosing the core 43. The recess in the base is sufficiently deep that thermal insulation 48 can be interposed between the plate and the core with its energizing winding thereon. The base can be made of material having a low resistivity such as aluminum, while the thin cap plate is made of a higher resistivity material such as steel so that current flow in the loop formed by the base member and the covering plate is most effective in translating the electrical energy into heat within the plate 42. The steel plate will generate heat due to both hysteresis and eddy current losses in addition to resistance losses due to the secondary current flow therein. The juncture between the base member and the cover plate 42 can be effected in zones of smaller cross-section formed by bevelling the base por= tions contacting the plate so that heat transmission to the base from the cover plate is minimized.

FIGURE 5 illustrates a fry pan unit utilizin gthe principles of the transformer construction of FIGURE 4 in which the exterior of the transformer remains cool while only the interior zones are raised to a relatively high temperature. In this connection, the core 53 is of flat annular shape with an insulated primary winding 54 Wound directly thereon extending over the full length of the annual and enclosed by the base 51 of thick cross-section forming a loop with an inserted flat plate member 52 having an upwardly extending wall 50. The outer shell formed of thebase 51 has an upwardly projecting overhanging lip section 55 while the plate member 52 inserted therein engages the interior of the lip 59 by way of its wall 50 to form an electrical loop therewith. The shell 51 also has a central projection 58 centrally engaging the under portion ofthe plate member 52, thereby forming a closed annular secondary loop about eachincrernent'of 33 so arranged about and 2 length of the core 53. The winding 54 on the core 53 has a pair of leads 55 extending through the wall of the shell 51 to a suitable connecting plug (not shown) on the handle 56 of the fry pan. Thermal insulation 57 is interposedbetween the core 53 and the bottom of the hot plate 52 to thermally insulate the core from the heating portion of the fry pan.

FIGURES 6 and 7 illustrate a kitchen-range type electrical heating element embodying the principles of this invention. The heating element here is shaped generally to look like those used in kitchen electrical ranges but utilizes magnetic principles in conjunction with the usual resistance heating principles to translate electrical energy into heat. An annular tube 61 of electrically conducting material encloses a core 63 of magnetic material electrically energized by a primary winding 64 connected to a pair of connecting prongs 65 adapted for association with a plug 66 connected to a source of electrical energy. The magnetic core is embedded within a high temperature resistant electrical insulating material such as a ceramic material 68 and can be laminated or in the form of a generally circular cable of wire conductors extending about the interior of the annular tube to form a complete annular magnetic core. The winding 64 generates magnetic flux in the core which cuts the circular wall of the tube to cause a current flow therein and consequently effect heating of the tube. For more efficient local transfer of heat to utensils placed thereon, the tube 61 is provided with a thin-walled upper portion or top 62 of material having a high electrical resistivity, thereby concentrating the heat in the upper zone of the annular loop 61 and correspondingly making it more quickly responsive in temperature to energy changes.

The primary winding d can be made of resistance wire such as Nichrome wire, which of itself will generate heat when energize-d in a manner simi ar to the electrical resistance heaters conventionally utilized. In addition to resistance heating, however, the tube in this arrangement translates magnetic energy into heat directly in the Walls of the tube 61 before heat is conducted thereto from the resistance wire through the insulating materials. Thus, a combination of resistance and magnetic heating of the tube 61is provided which is much quicker in startup than straight resistance-type heating elements, since heat is generated in the outerwalls as soon as electrical energy is supplied.

To reduce transfer of heat to the magnetic core 63 from the primary Winding, the core is provided with an electrical and thermal insulation covering 67 such asasbestos paper over which the energizing resistance winding 64 is wound. Both the magnetic core and the resistance wire are electrically isolated from the outer shell by the ceramic insulating material 68 within which they are embedded. Although resistance heating is here described, the primary can also be made to generate heat principally by current flow in the surrounding walls as in the arrangement of the foregoing embodiments. Where the resistance wire is utilized for the primary, however, the core may be more desirably disposed closer to the top of the space within the tube 61 so that the heat will be more readily conducted, through the heating surface from the resistance wire rather than to the side walls or the bottom.

FIGURE 8 illustrates a heating unit and the adaptability of the present invention to regulation by temperature control means without need for large power control elements. In this arrangement, the heating unit is an assembly of a closed loop secondary 102 of annular shape enclosing a magnetic core 103, beside being provided with a primary winding 104 within the secondary loop 102, has a second or control winding 105 which provides a saturating magnetic flux. The primary Winding 104 is energize-d in conventional manner by the line leads L1, L2. connected to a suitable source of alternating current, While the second winding 105 is connected to the line leads L1 and L2 through a rectifier 115 and bridge circuit. The second win-ding is energized by DC. under the control of a bridge circuit having an associated temperature sensing means such as a thermister connected therein. The magnetic flux generated by the primary winding 104 thus can be regulated in effectiveness to translate the electrical energy into heat by a setting of manually adjustable control components associated with the bridge.

The bridge circuit of FIGURE 8 is essentially 21 Wheatstone bridge type circuit having a thermister or other temperature sensing element such as a thermocouple 117 connected therein, while the remaining bridge resistances 113, 119, and are connected so that setting of the variable resistance 118 will determine the amount of en engy converted into electrical power in the closed secondary 102, and correspondingly fix the degree of temperature rise and temperature of the tube 102. The thermocouple is positioned on a section of the secondary which is representative of the temperature of the heating unit, and by setting the variable resistance 118 to a temperature setting determined by calibration, the balance of current flow in the bridge determines the saturating DC. current flowing in the winding 105. The resistance 118 can be accurately calibrate-d for temperature to be maintained at the heating unit so that when a temperature setting is made, a DC. magnetic flux will be generated in the core such as will permit generation of the proper amount of flux due to current flow in the winding 104 corresponding to the desired temperature.

Saturation of the core 103 by the second winding 105 can be carried to a value such that little or substantially no heating of the secondary tube 102 will occur. On the other hand, the setting can be adjusted so that the degree of saturation by the DC winding 105 is nil to permit full translation or" theelectrical energy of the winding 104 into heat energy in the tube 102. Thus, with a single setting of the relatively low current capacity resistance in the bridge circuit, the larger current of the secondary tube and translation of electrical energy into heat within the system can be fixed.

This bridge arrangement however, is only exemplary of one of many bridge control arrangements which can be adapted to the units of the present invention. For example, impedance type bridges, as well as any number of other type of electrical bridge networks can be utilized with a temperature sensing mechanism to provide saturation controls for setting temperature of the heating unit.

In view of the foregoing, it will be understood that many variations of the present invention can be provided within the broad scope of the principles embodied therein. For example, the transformer, although as illustrated, is predominantly adapted to use for heating units, it will be recognized that the transformer construction as illustrated in FIGURE 1 can be utilized for other magnetic circuit arrangements, such as provision of an energizing circuit for still another loop extended through the opening in the annular configuration illustrated. The magnetic fiux concentration in the secondary, and about the secondary of the construction is also of novel character, and any number of adaptations of the transformer principles here disclosed can be accomplished. Thus, while particular embodiments of the invention have been shown and described, it is intended by the appended claims to cover all such modifications which fall within the true spirit and scope of the invention.

I claim:

1. An induction heating apparatus of the character disclosed comprising in combination, a magnetic core having length in the form of a loop closed upon itself, a primary Winding wound upon said core, and an electrically conductive secondary loop closed about the cross-section of said core and extending over the full length of said core, the opposing side portions of said closed conductive loop within the space surrounded by said core forming a common portion of said conductive loop, and portions of said conductive loop along its length and located on one side a loop closed upon itself,

of said core loop having a reduced cross-sectional dimension and providing a surface dispose-d generally in a common plane for selective concentration of heat at said surface upon energization of said core.

2. An induction heated hot plate unit comprising a metallic plate member providing a major surface to be heated, a magnetic core in the form of a loop closed upon itself aligned adjacent the opposite major surface of said 1 plate member, an electrical primary winding on said core,

a housing for said core of conductive material joined electrically to the central region of said opposite surface side of the plate member bounded by said core loop and extending radially outwardly therefrom in all directions about the cross-section of said core loop and joined again on the outside of said core loop to said opposite surface side of said plate member to thereby form a closed electrical secondary path about the cross-section and length of said core loop, the plate member portions of said electrical secondarry path about said core being higher in resistance than the resistance of the remaining portions of said secondary path, whereby said plate member portions of said secondary become selectively heated to the highest temperature at its heating surface subject to energization of said primary winding.

3. An induction heated hot plate unit comprising a metallic plate member, a magnetic core in the form of a loop closed upon itself aligned adjacent one major surface of said plate member, an electrical primary winding on said core, a housing for said core of conductive material joined electrically to the central region of said plate member bounded by said core loop and extending radially outwardly therefrom in all directions about the cross-section of said core loop and joined on theoutside of said core loop to the back of said plate member to thereby form a closed electrical secondary path about the cross-section and length of said core loop, the plate member portions of said electrical secondary path about said core being higher in resistance than the resistance of the remaining portions of said secondary path, whereby said plate member portions of said secondary become selectively heated to the highest temperature subject to energization of said primary winding, the exposed surface of said plate member opposite said one major surface having angularly upwardly extending edge portions to form walls of a container for which said plate provides the bottom of said container.

4. An induction heated hot plate unit comprising an upper plate member of electrically conductive material, an underlying magnetic core having length in the form of a primary winding wound upon said core, an underlying housing about said magnetic core of electrically conductive material forming with said plate member a closed electrical secondary circuit about the cross-section of said core over the full length of saidloop, said housing being electrically joined to the underside of said plate member within the area bounded by said core loop and extending about said core loop to electrically join the underside of said plate memberagain at its edge regions to thereby form saidse-condary circuit, 1

the plate member portions of said electrical secondary path being higher in resistance than the'resistancc of thean annular magnetic core residing in said recess, a primary winding for energization of said core, said plate member and base being joined to form a closed electrical secondary circuit about said magnetic core, the walls of the base" portions of said secondary c1rcuit being thicker than said plate member portions of said secondary circuit whereby said plate member portions become selectively heated to a higher temperature upon energization of said core.

6. An electromagnetic heating unit of the character disclosed comprising in combination a magnetic circuitin the form of a loop closed upon itself, means for energizing said magnetic circuit loop, an electrically conductive loop closed about the cross-section of said magnetic circuit and extending over its full length, the opposing side portions of said closed conductive loop within the space surrounded by said magnetic circuit forming a common path in said conductive" loop, and portions of said conductive loop along its length and located on one side of said magnetic circuit loop being higher in resistance than'the resistance of the remaining portions of said closed conductive loop, said higher resistanceconductive loop portions presenting a heating surface disposed generally in a common plane for selective concentration of heat at said surface upon energization of said magnetic circuit.

References Cited by the Examiner UNITED STATES PATENTS RICHARD M. WOOD, Primary Examiner. L. H. BENDER, Assistant Examiner. 

1. AN INDUCTION HEATING APPARATUS OF THE CHARACTER DISCLOSED COMPRISING IN COMBINATION, A MAGNETIC CORE HAVING LENGTH IN THE FORM OF A LOOP CLOSED UPON ITSELF, A PRIMARY WINDING WOUND UPON SAID CORE, AND AN ELECTRICALLY CONDUCTIVE SECONDARY LOOP CLOSED ABOUT THE CROSS-SECTION OF SAID CORE AND EXTENDING OVER THE FULL LENGTH OF SAID CORE, THE OPPOSING SIDE PORTIONS OF SAID CLOSED CONDUCTIVE LOOP WITHIN THE SPACE SURROUNDED BY SAID CORE FORMING A COMMON PORTION OF SAID CONDUCTIVE LOOP, AND PORTIONS OF SAID CONDUCTIVE LOOP ALONG ITS LENGTH AND LOCATED ON ONE SIDE OF SAID CORE LOOP HAVING A REDUCED CROSS-SECTIONAL DIMENSION AND PROVIDING A SURFACE DISPOSED GENERALLY IN A COMMON PLANE FOR SELECTIVE CONCENTRATION OF HEAT AT SAID SURFACE UPON ENERGIZATION OF SAID CORE. 